Some vehicles employ passive entry systems, in which a controller provided in the vehicle periodically polls for key FOBs (hereinafter referred to as either FOBs or key FOBs) in the vicinity of the vehicle, and to allow entry into the vehicle (e.g., by unlocking a locked door) when an appropriate key FOB is detected. A vehicle passive entry system operates by sensing a door handle operation, such as when a person attempts to open a door. Upon such a sensing, the passive entry system then polls for any key FOBs in the vicinity of the vehicle, by outputting a low frequency (LF) signal), which corresponds to a FOB interrogation signal. The key FOBs in the vicinity of the vehicle respond to this interrogation signal by outputting an ID signal, which is received by a receiver of the passive entry system. When an ID of a key FOB assigned to an allowed vehicle operator is detected, the door upon which the door handle operation was sensed is opened from a locked state, thereby allowing passive vehicle entry.
A problem occurs in conventional vehicle passive entry systems when more than one FOB responds to the interrogation signal output by the passive entry system. This simultaneous response by more than one FOB results in data collision at the receiver of the passive entry system. Due to the collision of data, the passive entry system cannot properly decode the data, and it cannot determine whether or not the person attempting to open the vehicle door is an authorized person.
To solve the above problem, one conventional approach is to preprogram a delay for each FOB to respond to an interrogation signal, so that the likelihood of data collision is minimized. Thus, for a vehicle having two vehicle operators, each with their own FOB, the first vehicle operator's FOB is programmed to respond immediately to a passive entry system interrogation signal, whereby the second vehicle operator's FOB is programmed to respond after a preprogrammed delay, e.g., 10 millisecond delay. The preprogrammed delay allows for enough time such that there is no possibility of data collision of data output by the second vehicle operator's FOB with respect to data recently output by the first vehicle operator's FOB. However, such a system suffers in that the response time for opening a vehicle door is necessarily increased due to the preprogrammed delays built into to each FOB, whereby such a delay may be fairly large when a number of allowable FOBs (e.g., 50 or more) are assigned to authorized vehicle operators.